Pituitary hormones released during sexual maturation of the rat appear to influence the rate of retinal degeneration after exposure to continuous photoperiod. Retinas of young, sexually immature rats are more resistant to damage by radiant energy than those after sexual maturity (6 to 8 weeks of age). Preliminary studies from this laboratory have shown that hypophysectomy (HYPEX), which inhibits sexual maturation and influences pituitary target organs, exerts a "protective influence" on retinas exposed to continuous radiant energy. The retinas of HYPEX rats do not degenerate as rapidly as those of adult, intact rats. Ovariectomy of rats inhibits the damaging effect of photoperiod exposure. The effects of the pituitary gland and the gonads on photically-induced retinal damage will be examined further in hypophysectomized and intact rats of different ages after the administration of pituitary extracts, pituitary transplantation, and substitution therapy with pituitary gonadotrophins. Additional studies will involve an analysis of retinal damage after overiectomizing rats of different ages and substitution therapy with ovarian steroids prior to and during exposure to cyclic photoperiod, low-intensity visible radiant energy, or high-intensity radiant energy. BIBLIOGRAPHIC REFERENCES: O'Steen, W.K. An Influence of the Pituitary Gland on Photically-Induced Retinal Photoreceptor Degeneration. Anat. Rec., 184: 194,1976. An Abstract. Olafson, R.P., and W.K. O'Steen. Reduced Retinal Photoreceptor Damage in Hypophysectomized and Ovariectomized Albino Rats. Invest. Ophthal., 1976, in press.